Update README to include information about algorithm used.

More readable.

README.md

@@ -1,6 +1,8 @@
 # Indivisible
 
-Indivisible is an optimized prime number generator and tester.
+Indivisible is an optimized prime number generator and tester using a segmented
+version of the [Sieve of
+Eratosthenes](https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes).
 
 ## Build & Installation
 

benchmark.sh

@@ -21,6 +21,7 @@ do
 	case "$opt" in
 		s)
 			OPTIONS=("${OPTIONS[@]}" -s "$OPTARG")
+			SIEVE=$OPTARG
 			;;
 		t)
 			TRIALS="$OPTARG"
@@ -33,6 +34,8 @@ do
 done
 
 echo "Calculating primes up to 1,000,000,000"
+echo "Trials: $TRIALS"
+echo "Sieve segment size: ${SIEVE:-"default"}"
 TOTAL="0"
 for _ in $(seq "$TRIALS")
 do

src/worker.rs

@@ -19,6 +19,7 @@
 /**
  * @brief Work on a segment.
  *
+ * @param known_primes:&Vec<u64> List of known primes at least until sqrt(end).
  * @param start:usize Beginning of the segment (inclusive).
  * @param end:usize End of the segment (exclusive).
  *
@@ -28,8 +29,14 @@ pub fn work_segment(known_primes:&Vec<u64>, start:usize, end:usize) -> Vec<u64>
 	let mut sieve = vec![true; end - start];
 	let mut found_primes = Vec::new();
 
+	let sqrt_end = (end as f64).sqrt() as usize;
+
 	for p in known_primes {
 		let prime = *p as usize;
+		if prime > sqrt_end {
+			break;
+		}
+
 		let modu = start % prime;
 		let mut mult = if modu == 0 {
 			start

test.sh

@@ -17,7 +17,7 @@ fi
 tests=0
 passed=0
 
-## TEST 1
+## TEST
 ((tests++))
 echo -n "${tests}: Find all prime numbers before 70..."
 expect="2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 "
@@ -30,7 +30,20 @@ else
 	echo " FAIL"
 fi
 
-## TEST 2
+## TEST
+((tests++))
+echo -n "${tests}: Find last prime before 1,000,000,000..."
+expect="999999937"
+
+if [ "$("$BINARY" 1000000000)" = "$expect" ]
+then
+	echo " pass"
+	((passed++))
+else
+	echo " FAIL"
+fi
+
+## TEST
 ((tests++))
 echo -n "${tests}: 11 is prime..."
 if "$BINARY" -t 11
@@ -41,7 +54,7 @@ else
 	echo " FAIL"
 fi
 
-## TEST 3
+## TEST
 ((tests++))
 echo -n "${tests}: 9 is not prime..."
 if ! "$BINARY" -t 9
@@ -54,3 +67,8 @@ fi
 
 ## RESULTS
 echo "Results: $passed/$tests"
+
+if [ $passed -ne $tests ]
+then
+	exit 1
+fi